1. Field of the Invention
The present invention relates in general to techniques associated with a mold for molding a disk, more precisely, a substrate of a compact disk (CD), a digital video disk (DVD), a magneto-optical disk, a phase-changing optical disk, or the like. More particularly, this invention is concerned with a mold which is provided with a plurality of air blow passages through which a stream of compressed air is introduced into a mold cavity, to facilitate removal of a molded disk substrate from the mold.
2. Discussion of the Related Art
There have recently been used optical disks and other disks as a data storage medium in various fields of the art. Disk substrates used for producing these disks are produced by a known mold, for example, by using a mold including a stationary mold half and a movable mold half, both of which have respective molding surfaces cooperating to define therebetween a mold cavity. The stationary and movable mold halves are brought to a closed position to define the mold cavity, and a material of the disk substrate is injected into the mold cavity. As a result, the disk substrate is molded. Then, the stationary and movable mold halves are brought to an open position, while the molded disk substrate is retained on the molding surface of one of the stationary and movable mold halves. The molded disk substrate is removed from the mold half by using a suitable mechanism, such as a mechanical ejector and an air blow device. Thus, the desired disk substrate is produced. The air-blow device is adapted to supply compressed air to the mold cavity for facilitating removal of the molded disk substrate from the mold cavity. This device is effective not only to aid the mechanical ejector to remove the molded disk substrate, but also to prevent local damage or deterioration or local sticking of the disk substrate in the process of cooling of the material in the mold cavity. Hence, the air blow device is preferably employed.
The air blow device is generally provided for at least one of the stationary and movable mold halves such that an air passage is open on the molding surface of the stationary or movable mold half, at two or more outlets located at the suitable circumferential positions of the mold half. To facilitate the removal of the molded disk substrate from the mold half, compressed air is fed into the mold cavity through the air outlets open on the molding surface of the mold half.
An extensive study of the air blow device by the present inventor revealed that the quality of the disk substrate is influenced by arrangement of the air blow device. Especially, the production. of the disk substrate used for a DVD which has a relatively thin thickness in comparison with those of a CD and a CD-ROM is significantly influenced by the arrangement of the air blow device. For instance, the molded disk substrate suffers from bending or buckling due to inadequate air blows, resulting in an increased ratio of reject of the molded disk substrate.
A further study of the known air blow device in an effort to solve the above-described problem revealed that a variation of pressure of the compressed air injected from the air outlets may cause partial or local sticking of the molded disk substrate to the molding surface upon removal thereof from the mold half, so that the corresponding local area of the molded disk substrate tends to be bent or buckled, and otherwise deteriorated.